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Discussion Starter #1
Here is the run down.

I drove the car to Taco Bell, around 3 miles from my house, in December. While sitting in the drive through I noticed my battery light came on.
Drove it home and didn't really look into it. That day was unseasonably warm.

So when I started working on the problem this is how it went.

Silly me - I exchanged my alternator that I had just replaced not 200 miles ago without checking the fuse. Put the new one in, battery light still on.
Checked the fuse and was elated. Cool. I found the issue. NO.

Replaced the fuse, took the car for a drive and battery light again.

Popped the fuse.

Note: The fuse will only pop once the car is warmed up and rev'ed to above 3000RPM. I can leave the car sit at idle for as long as I want and the fuse will not pop and the regulator charges the battery.

I went back to Autozone and they upgraded me to Duralast Gold instead of the cheapo I started with.
Alas that didn't work either.
At this point I got the meter out and started checking.
Alternator body to negative terminal - 0 ohms
Alternator charging post to Positive terminal - 0 ohms
Regulator Pig tail wire# 36 from connector to fuse box - 0 ohms

Got looking into the print and there is a connector BEFORE the fuse box named "c100" in the print. I took wire#36 and bypassed that connector just to be safe.

I have checked the seating of the pin inside the fuse box itself. The main "lug" on the fuse box is a little wonky. It looks like someone spun the nut at one point but I have good connection non the less.

So in summary.
I have replaced the pigtail to the regulator.
I have removed the fusable link and replaced it with a new fuse of the correct rating.


I have yet to replace the charging cable itself. The ohm reading on the cable is 0.00. I did check for voltage drop in that cable when I first started this adventure a couple months ago.

I ordered the black and white regulator connector today as well as a new charging cable. I'll update once those are installed.

I don't really want to have to purchase a motorcraft alternator but I am wondering how many bad ones from AutoZone I can get.

How likely is it that it is still the alternator?

Thanks!
 

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which fuse is or fuse link is blowing?
 

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Discussion Starter #3
Just the 20 amp alternator fuse in the fuse box.

I just got confirmation the charging cable was delivered today I’m going to install that and see where it gets me.


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you need to supply the rest of the circuits

marked in the triangles. A and B

or just keep throwing parts at it, your money
 

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Discussion Starter #5
How do you mean supply the rest of the circuits.
That’s what the fuse box does. I have no other issues with any other circuits.

The ALT fuse is the first fuse in the circuit of the fuse box, and the following 3 are all rated above 20A.

Not trying to throw money away, I’m trying to solve the problem.
I’ve spent 11 years in industrial maintenance I understand electricity on a fundamental basis just fine.

Post just to post though. Thanks.



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Discussion Starter #6
Also those circuits marked A and B are for the 4v motor. The entire circuit for that fuse is pictured in the PDF.


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you did NOT state what vehicle you are working on, just because you posted in this section, means nothing

so you dont have a 4v, very well

in order for you to over amp that fuse, either the conductor or the alt is shorted to ground

use a test light to find the short.
 

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So you are blowing the fuse marked ALT 20A, correct? Put your amp clamp by the fuse and verify you have more than 20A draw. Idle vs. 3,000 rpm, your draw should not matter, since as the rpms climb, you should see the draw stay the same. Step 1 is to confirm you are indeed pulling current more than what the fuse is rated for. The other culprit is on the regulator side. A bad reference for the regulator will cause voltage to climb, and thus current.
 

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Discussion Starter #9
I apologize I did not realize my post did not include make and model. My username is 98GT, and I just joined.

As far as a short that’s pretty obvious or else the fuse wouldn’t be blowing...
No offense man but your answers are common sense I am hoping by posting on here that someone who has experience with the cars can lead me down the correct path.
For being new to the forum and you being a top contributor it’s pretty obvious that title comes from short responses without any actual advice.

A test light is about the worst possible way I can picture to find a short. I have meters and amp clamps.



I can verify amp draw indeed climbs with the revs. Over the 20amp rating on the “sense” wire.

I’ve read and read on this issue, I’ve come across people who try 6 different alternators until it works.
I’m just hard pressed to believe that many alternators could be bad from auto zone.

I am replacing the charging cable from alt to fuse box tonight.
I want to eliminate any wire degradation, since process of elimination is the only troubleshooting process I can follow right now.


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Discussion Starter #10
Update :

Changed the charging wiring harness.

Everything from the alternator to the fuse box is new MINUS the connection inside the fuse box. I could bypass it to eliminate the connection but I highly doubt that’s the problem.


Tomorrow I will acquire another alternator.
I’ll ask to have them bench test it before I leave.

I can not find a motorcraft for under $400. Im going to sleep on purchasing that or going to a parts store other than AutoZone. Duralast has definitely put a sour taste in my mouth.
Unfortunately my receipt for the one I have has been misplaced I moved and I can’t find it.

I also triple checked my grounds.
Block ground in the front drivers side is good, block ground in the back is good.


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Discussion Starter #11
Replaced the alternator with a new one.
No more issues.

To anyone arguing with this issue start with new or OEM parts.


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